i2c: pm_smbus: check smb_index before block transfer write

While performing block transfer write in smb_ioport_writeb(),
'smb_index' is incremented and used to index smb_data[] array.
Check 'smb_index' value to avoid OOB access.

Note that this bug is exploitable by a guest to escape
from the virtual machine. However the commit which
introduced the bug was only made after the 3.0 release,
and so it is not present in any released QEMU versions.

Fixes: 38ad4fae43 i2c: pm_smbus: Add block transfer capability
Reported-by: Michael Hanselmann <public@hansmi.ch>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Michael Hanselmann <public@hansmi.ch>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 20181206121830.6177-1-ppandit@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/hw/i2c/pm_smbus.c b/hw/i2c/pm_smbus.c
index 685a2378ed95e63ff5f275adeaa737a6125fa504..03062740cc93c555567c3b75f83c7fb7acbec545 100644 (file)
--- a/hw/i2c/pm_smbus.c
+++ b/hw/i2c/pm_smbus.c
@@ -240,6 +240,9 @@ static void smb_ioport_writeb(void *opaque, hwaddr addr, uint64_t val,
             uint8_t read = s->smb_addr & 0x01;
 
             s->smb_index++;
+            if (s->smb_index >= PM_SMBUS_MAX_MSG_SIZE) {
+                s->smb_index = 0;
+            }
             if (!read && s->smb_index == s->smb_data0) {
                 uint8_t prot = (s->smb_ctl >> 2) & 0x07;
                 uint8_t cmd = s->smb_cmd;